Method of preparing quick-cooking rice



United States Patent METHOD OF PREPARING QUICK-COOKING RICE Harold A.Campbell, Denville, and Frank Hollis, Jr.,

Weehawken, N. .L, assignors to General Foods Corporation, New York, N.Y., a corporation of Delaware No Drawing. Application April 5, 1951,Serial No. 219,514

8 Claims. (CI. 9980) This invention relates to improvements in quickcooking dry rice.

Raw rice is sometimes marketed without removal of its bran coat as brownrice, but more often the bran coat is removed by milling to form theusual White or milled rice of commerce. In both cases the rice grainsare hard, dense and opaque and consist largely of raw starch having amoisture content of about 8-14%. During cooking of such rice, the starchis gelatinized and the moisture content of the grains increases to about65-80%, the grains swelling to several times their original size andbecoming soft and palatable. In order to make sure that the starch inthe centers of the grains is properly cooked, however, relatively longcooking is required with the result that the starch at the grainsurfaces becomes overcooked and the starch granules burst, discharging asticky pasty liquid. The surfaces of the grains are then pasty andunpalatable unless the starch paste is Washed off with a resulting lossof nutritive constituents which may amount to as much as 25% by weightof the rice. In order to avoid this undesirable surface overcooking, thecooking period must be shortened so much that the centers of the grainsare somewhat undercooked and tough and chewy. Even in this case,moreover, undesirably long cooking times are required.

The principal object of the present invention is to provide an improvedprocess for treating raw rice so that moisture can penetrate relativelyrapidly to the interior of the grain during cooking. Thus the grains canbe cooked uniformly throughout to render them soft and palatable at thecenter without surface pastiness, and at the same time the cookingperiod can be substantially shortened.

It has been found that when raw rice grains are subjected to radiantheating by exposing them to a suitable source of infrared radiation,numerous small cracks or fissures are produced which extend inwardlyfrom the surfaces of the grain. As a result, when the treated grains aresubsequently cooked, moisture penetrates rapidly to the interior of eachgrain through the cracks or fissures,

and the grain centers are cooked to the desired soft palatable conditionwithout any substantial amount of surface overcooking in a period onlyabout half as long as that required to cook the untreated raw rice.

The exact explanation for the production of the aforesaid cracks orfissures is uncertain. They may be due in part to the fact that the ricegrain is not homogeneous so that various sections thereof may havedifferent coefficients of expansion and unequal expansion may causecracking. 0n the other hand, the surface portions or layers of thegrains that are exposed to the infrared radiation heat up very rapidly,whereas transmission of heat therefrom through the rice grains to theirinteriors takes place more slowly. The resultant uneven heating of thegrains from the outer to the inner sections also tends to cause unequalexpansion and cracking.

The treated grains closely resemble raw rice on casual observation, theindividual grains having approximately the same size, shape andappearance as the untreated grains. On closer examination, however, andespecially when the treated grains are viewed under the microscope, thecracks or fissures are readily apparent and the grains have a segmentedappearance. The treated rice may be cooked in the same manner as the rawrice, but in about half the time, and the resulting product is uniformlycooked and soft and palatable throughout.

In treating the raw rice, any desired procedure can be used whereby theindividual grains are exposed to the in- "ice frared radiation for ashort period. Within wide limits of intensity of radiation, heatingtakes place so rapidly that the rate of heating is approximately thesame in all cases and hence cannot serve as a control factor. The onlyoutward manifestation of the extent of heating that can be usedpracticably for control purposes is the final surface temperature of therice grains. Insufficient heating, as manifested by too low a finaltemperature, will not produce sufficient cracking or fissuring to effectthe desired improvement in the cooking properties of the rice. Excessiveheating, as manifested by too high a final temperature, results in unduebreakage of the grains.

Hence the period of heating should be correlated with the intensity ofthe radiation to produce the proper surface temperature of the rice. Ithas been found that the temperature limits to be observed vary accordingto the moisture content of the raw rice. At a normal moisture content ofaround 10%, the final temperature of the rice should be between 170 F.and 250 F. At a moisture level of 18%, which is about the maximum forthe pres- I ent process, the final rice temperature should be between130 F. and 220 F. Drier rice can also be treated. At 6% moisture, whichis about the minimum for the present process, the final rice temperatureshould be between 190 F. and 260 F. As a rule, commercial rice has amoisture content in the range of 10-14% and is well suited for treatmentby the present process. Of course, such rice may be further dried beforetreatment, but no practical advantage is gained thereby.

In practice, the rice grains are preferably passed under :1 the infraredgenerator or generators in a moving stream or layer, the speed ofmovement of the rice being correlated with the intensity of theradiation to provide the desired final surface temperature. In order toinsure uniform results, the grains are preferably exposed in a layerthat is only about one grain thick and at the same time are agitated tocause overturning or rotation of the grains, care being also taken tomaintain approximately uniform intensity of radiation over the entireexposed area of the rice bed or layer. The intensity of the radiation atthe surface of the bed depends, of course, on the intensity at thesource and on the distance of the source from the bed.

By way of example, the rice is irradiated in a Jeffrey Vibrator-Feederlined with a stainless steel trough 3" Wide and 29 long. The action ofthe vibrator causes the grains to move along the trough in a bed, sheetor layer and at the same time to rotate about their axes. The grain isfed continuously to the feed end of the vibrator at a rate such that themoving bed or layer is approximately one grain thick. Four 250 wattinfrared lamps with built-in reflectors are aligned along the trough,facing downward at a distance of about 18" from the moving rice bed toprovide the desired infrared radiation. These conditions affordsubstantially uniform exposure of grain surface to the radiation.

As an example of the use of the above apparatus, raw

' white rice having a moisture content of 9.8% was passed through thevibrator three times in succession, each pass requiring 17 seconds sothat the total time of exposure was 51 seconds. At the end of the thirdpass, the surface temperature of the rice Was 208 F. as determined by aprobing type pyrometer, and numerous cracks or fissures had developed inthe grains as described above. 40 grams of the fissured rice was cookedfor 9 minutes in 5 cups of boiling water to produce an evenly cookedrice of good texture.

The process set forth above can also be combined very advantageouslywith the process of preparing quick cooking rice that is disclosed andclaimed in U. S. Patent No. 2,438,939. This prior process, brieflysummarized,

comprises precooking rice grains to increase their moisture content to-70%, and then drying the swollen grains rapidly to set them in theirenlarged size and to produce a porous structure so that rehydration ofthe dried product takes place rapidly on final cooking by t theconsumer. In the precooking operation, it is desirable usually are notcompletely gelatinized. in consequence, a minimum rehydration or finalcooking period of 2-3 minutes is required and the centers of the grainstend to be rather firm and somewhat chewy, a condition preferred by manyconsumers but considered undesirable by others. As explainedhereinafter, these difficulties of the prior process can be largely ifnot completely eliminated, and furthermore an improved product can beobtained, by combining the radiant heating method de scribed above withprecooking and drying steps similar to those described in the aforesaidpatent.

in the prior process it is preferred to so the raw rice prior toprecooking in order to facilitate precooking operation and to promotethe formation of voids in the dried product. When the rice is first crabor fissured by radiant heating, however, substantially uniform andcomplete gelatinization can be effected during precooking withoutpreliminary soaking. Hence soaking is unnecessary and in fact isundesirable when the rice is precooked by immersion in hot or boilingwater because it leads to the production of an undesirable soft, sor ypro t. On the other hand, when the rice is precooaed by See 1- ing, somepreliminary soaking is advantageous to distribute moisture substantiallyuniformly throughout the rice grain, but the average soaking time may bedecreased as much as 50% as compared with the prior process and yet theaverage water imbibition may be increased from 30% to about 45%.

Whether the cracked rice is precooked by immersion in boiling water orby steaming, gelatinization t kes plaec uniformly throughout the grainand practically complete gelatinization can be effected without dangerof surface overcooking with its consequent undesirable characteristicsof pastiness and loss of solids. Thus the Water uptake of the rice canadvantageously be increased beyond that preferred in the prior process,the moisture content of the precooked rice preferably being at least7645 Accordingly the volume of the precooked rice is about greater thanthat resul"' from the preferred practice of the prior process, and t .efinal product obtained on drying this bulkier rice has improvedproprties upon reconstitution as will be pointed out he. after. Afurther important advantage is that the store said more complete cooring may be carried out in substantialy less time than that previouslyrequired; for example, complete gelatinization can be ob ained bycooking in boiling Water for about 10 minutes zithout preliminarysoaking, as compared with l2--l4 minutes usually required even afterthorough soaking.

After precooking it is usually desirable to cool the rice to preventfurther gelatinization as disclosed in t e aforesaid patent, either byexposing the precooked .e to a last of cold air or preferably byimmersing it in cold water. The latter method has the additional advantge of washing any foreign material from the cooked rice, and since thereis little or no surface overcocking, no appreciable quantity of solublesolids is removed by such washing.

After the precooked rice has been cooled, it is next subjected to rapiddrying which, as described in the aforesaid patent, removes moisturefrom the surfaces of the grains at a rate sufficiently faster than itcan diffuse thereto from their interiors as to set them in theirenlarged condition and produce a porous structure therein. As a resultof preliminary cracking or fissuring, however, the rice dries at a much.faster rate. Using apparatus similar to that described in the priorpatent, the fissured rice can be dried satisfactorily in about twothirds of the time needed for rice which is not fissured. This resultsfrom the fact that the rice grains are bulkier as explained above andhence have greater surface area from which moisture can be removed, andfrom the further fact that said fissures provide additional exits toremove the water from the centers of the grains to their surfaces.Moreover, because of the greater bulk of the precooked grains and themore rapid drying thereof, the dried product is bulkier and flufiierthan similar products heretofore pro duced, being to 50% greater in bulkthan that obtained in the preferred operation of the prior process.

Best drying results are obtained by spreading the moist rice on asupporting screen and blowing relatively dry heated air upward throughthe rice, whereby the grains are agitated and separated to preventmatting and to insure thorough air circulation around each grain. Withappropriate air velocity and humidity, drying maybe carried out at roomtemperature but it is usually preferable to accelerate drying by heatingthe air, temperatures greater than about 140 C. being avoided to preventscorching of the rice. In most cases it is sufficient 5 to dry the riceto about 8 to 14% moisture, but if desired,

such rice may be dried to a lower figure.

As a result of its greater size, substantially uniform and completegelatinization, and greater porosity, the quick cooking dry riceprepared in the above manner is superior upon rehydration to any suchproduct prepared heretofore. in particular, the rice is quicker cooking,requi ng as little as 2 minutes in many cases, but the rehydiated orcooked rice also has greater bulk volume and is fluffier and as a resultmore palatable than similar products heretofore produced; it is alsoless pasty and substantially devoid of tough, chewy centers;furthermore, upon rehydration or final cooking the product takes up agreater volume of water and its moisture content closely approaches thatof the precooked rice prior to drying.

As an example of the combined process set forth above, the cracked orfissured ice of the example set forth above is passed into a continuouscooker comprising a rotary reel of the pea blancher type, in which therice is precooked '11 water at a temperature of about 269 for it)minutes. At the end of this time the rice is uniformly and almostcompletely gelatinized and has a moisture content of 72%.

The rice is then discharged into a whirlpool type washer supplied withcold water entering at 60 F. and is cooled to about 76 F. in about 2minutes. This washing also removes any foreign material present in therice.

The cooled washed rice is then fiumed onto a v r screen conveyor belt todrain off excess water, being placed on the belt in a 3 inch layer andallowed to drain l or 5 minutes.

The drained rice is then deposited on a continuous c nveyor drier belpassing through a forced draft drier 50 fee: in length feet width. Thelayer of rice is about 1 inch th and air is forced upwardly anddownwardly throug the rice bed at an air inlet temperature of 250 F. andan air velocity of 175 eet per min The rice passes through the drier inminutes .e. its moisture content is reduced to 11%.

One hundred forty-two grams of the dried rice is reconstituted bypouring 475 ml. of boiling water thereon. After allowing 5 minutes ofstanding, the rice is rehydrated to provide a soft, non-pasty,substantially uniformly gelatinized cooked rice having a moisturecontent of 72%.

it will be understood that the invention is not restricted to thedetails of the foregoing description nor to the examples particularlyset forth therein, and that reference shouldbe had to the appendedclaims for a definition of its lnnits.

' k cooking dry rice rice ains to h .d cause beyond their oi ns by rcmovctently faster 2. process 0. it comprises 5 ared rad ation subjectingthe c said rice rice grains are from their 5 aces at a rate so theretofrom their ed condition and I unbroken raw rice grains to ared radiationto iJrGVid'Q said rice grains with llssurcs, ..en cooking the fissuredrice grains in water to gelatinize the starch and raise its moisturecontent to at least about 70-75% with substantial swelling of the grain,then cooling the grains to prevent further gelatinization of the starch,and then drying the swollen grains by removing moisture from theirsurfaces at a rate sufiiciently faster than it can diifuse thereto fromtheir interiors as to set them in their enlarged condition and produce aporous structure therein.

4. A process of preparing a quick cooking dry rice which comprisessubjecting unbroken raw rice grains to infrared radiation to providesaid rice grains with fissures, then cooking the fissured rice grains inwater to gelatinize the starch and raise its moisture content to atleast about 7075% with concomitant substantial swelling of the grain,and then drying the grains by circulating heated air through the grainsto remove moisture from their surfaces at a rate sufliciently fasterthan it can diffuse thereto from their interiors as to set them in theirenlarged condition and produce a porous structure therein.

5. The method of producing quick cooking rice which comprises subjectingunbroken raw rice grains containing 6-1S% moisture to infrared radiationto raise the surface temperature of the grains to a value within therange of 130 F. to 260 F., then subjecting the treated grains to theaction of moisture and heat to gelatinize the starch with concomitantsubstantial swelling of the grains, and then drying the swollen grainsby removing moisture from their surfaces at a rate sufliciently fasterthan it can diffuse thereto from their interiors as to set the grains intheir enlarged condition and produce a porous structure therein.

6. The method of claim 5 wherein the gelatinized grains are cooledbefore being dried.

7. The method of claim 5 wherein the grains are dried by circulatingheated air therethrough.

8. The method of claim 5 wherein the grains are cooked in water togelatinize the starch and increase the moisture content of the grains toat least 70-75 References Cited in the file of this patent UNITED STATESPATENTS Number Name Date 1,094,197 Davis Apr. 21, 1914 1,850,123Anderson Mar. 22, 1932 2,428,090 Naeher et a1 Sept. 30, 1947 2,438,939Ozai-Durrani Apr. 6, 1948 FOREIGN PATENTS Number Country Date 578,614Great Britain July 4, 1946

1. A PROCESS OF PREPARING A QUICK COOKING DRY RICE WHICH COMPRISESSUBJECTING UNBROKEN RAW RICE GRAINS TO INFRARED RADIATION TO PROVIDESAID RICE GRAINS WITH FISSURES, THEN SUBJECTING THE FISSURED RICE GRAINSTO MOISTURE AND HEAT TO GELATINIZE THE STARCH AND CAUSE THE GRAINS TOSOFTEN AND SWELL SUBSTANTIALLY BEYOND THEIR ORIGINAL SIZE, AND THENDRYING THE SWOLLEN GRAINS BY REMOVING MOISTURE FROM THERETO FROM THEIRINTERIORS AS TO SET THEM IN THEIR ENLARGED CONDITION AND PRODUCE APOROUS STRUCTURE THEREIN.